There is a death showing for a Mary Lewis, aged 28, Q1, Montgomery. I'm not sure about this but am it putting up as a possible. Birth reg of Mary Ellen could have been s few weeks late.
The following is what I've found on the Bangor on Dee couple. I've not found a suitable marriage for a James Lewis and a Mary Davies, so far but could have overlooked it.
Mary Lewis, died, aged 57, May/June 1872 and was buried 4 June Bangor on Dee
The Bangor on Dee James re married a Margaret Peers 5 Oct 1872, Bangor on Dee:
James, 53,widr, a fruit dealer, Father John Lewis, a Gentleman
Margaret, 43, wid, Father John Evans, a Cattle Dealer.
James bpt, Llansanffraid Y M, Montgomeryshire. on 5th Oct 1818. to John (farmer) and Mary Lewis
James, aged 65, died March 1884 and was buried 31 March 1884, Bangor on Dee
I've not found parents on the US censuses so

?
Have you seen any traces of them, Sandra?
Gadget